The purpose of this study is to examine the events involved in calcitonin biosynthesis. To address this question we will utilize the techniques of molecular biology to pursue a number of interrelated studies examining the structure and regulation of expression of the calcitonin gene. In addition, we will begin an in-depth study of calcitonin biosynthesis in human tumors which have been shown to synthesize and secrete this hormone ectopically. Finally, calcitonin DNA sequences which code for the hormonal precursor will be introduced into cultured cell lines where the processing and maturation of peptide hormones from this larger precursor can be studied. These studies will provide insights into the molecular mechanisms of calcitonin biosynthesis and permit a better understanding of how endocrine tissues synthesize and process gene products which are destined for secretion.